i

Acknowledgements

The Ministry of Agriculture, Mechanization and Irrigation Development (AMID) is highly indebted to the Food and Agriculture Organization (FAO) of the United Nations for providing the technical and financial resources for the development and subsequent reproduction of the Conservation Agriculture (CA) Module for use by students studying for the Diploma in Agriculture.

The contribution of Sepo Marongwe, the National CA focal person from AGRITEX and the Chief Agricultural Education Officer in the Department of Agricultural Education and Farmer, Mr. Francis Borgia Vengai is greatly appreciated, especially during the drafting and collection of information on Conservation Agriculture.

Special mention goes to the FAO Zimbabwe office for inviting comments from a wide spectrum of experts in Conservation Agriculture including those from FAO Head Office in Rome. All these comments contributed immensely to the final form and character of the CA module.

We would also like to thank all members of the Conservation Agriculture Taskforce for their valuable contribution in the provision of information and comments during review meetings.

Many thanks also go to the following individuals; institutions and government departments who were involved in the review of the CA Module: Principles of Agricultural Colleges; The Institute of Environmental Studies; Departments of Agricultural Education and Farmer Training; Agricultural, Technical and Extension Services; Mechanization and Irrigation Development; Research and Specialist Services; Economics and Markets; and the Department of Veterinary Services and Livestock Production.

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FOREWORD

I am pleased to write this foreword for the Conservation Agriculture module that has beendrafted for the diploma level students in agriculture colleges. The main objective of this module is to impart basic concepts of conservation agriculture to agricultural students whoare eventually destined to work with all categories of farmers.

Up to this point, the teaching of conservation agriculture was not clearly defined. Lecturerscovered the subject according to their own perceptions. There was no standard reference text or manual that was designed for use by agricultural students. This gap has now been filled by this module.

This module or manual is important in the main highlights of conservation agriculture arediscussed and there are set activities that will assist the student to grasp the critical principles of the subject. These principles are minimum mechanical disturbance of the soil, the use of mulch to cover and protect the soil surface, the use of appropriate croprotations and finally improved management practices. Several farmers have implemented these principles of conservation agriculture and have achieved tangible success. Conservation agriculture has definitely a part to play in our agricultural sector, especially in view of the threats posed by climate change.

I encourage all students to use this module thoroughly and apply the recommendationsfor the benefits of our farmers.

N MASOKASECRETARY FOR AGRICULTURE, MECHANISATION ANDIRRIGATION DEVELOPMENT

CONTENTS: Page

1. Chapter 1: Introduction To Conservation Agriculture 2

Aim 2

Objectives 2

Definition of term Conservation Agriculture(CA) 2

Conservation Agriculture Principles, Advantages and Challenges 4

Activities 9

References 9

2. Chapter 2: Conservation Agriculture Options and Appropriate

Technology 10

Aim 10

Objectives 10

Manual Conservation Agriculture Tillage Systems 10

Ox-drawn Conservation Agriculture Tillage Systems 13

Tractor-Drawn CA Tillage Systems 14

Activities 16

References 27

3. Chapter 3: Crop and Livestock Interactions in Conservation

Agriculture 18

Aim 18

Objectives 18

Agricultural Ecosystem 18

Competition for Crop Residues 20

Transfer of Plant Nutrients 21

Draught Power Requirements 21

Competition For Land 21

Livestock Manure and Compost as Alternative Fertilizer in

Conservation Agriculture 21

Activities 23

References 24

1

(4hrs Theory & 8hrs Practical)

1.1 Aim: To acquaint students with the concept of conservation agriculture, the historical aspects and

the principles of conservation agriculture

1.2 Objectives: At the end of this topic, the students will be able to

i. Define the term conservation agriculture

ii. Appreciate the historical aspects of conservation agriculture

iii. Discuss the conservation agriculture principles, their benefits and problems

1.3 Definition of the term conservation agriculture

Conservation agriculture (CA) is a way of farming in which the main objective is to utilize land and other

resources in a sustainable manner. The word “conservation” itself implies careful and judicious use of

resources to retain and eventually enhance them and this is the core message in conservation

agriculture.

While conservation agriculture has been practiced by farmers all over the world in many different ways, it

is only in recent times that it has become to be regarded as a discipline which requires attention like any

other discipline in agriculture.

As a discipline, conservation agriculture advocates minimizing soil disturbance, reducing soil loss,

improving water conservation and practicing farming methods that are sustainable and less damaging to

the overall environment.

The Food and Agriculture Organization (FAO) defines conservation agriculture as “a way of farming that

conserves, improves and makes more efficient use of natural resources through integrated

management of the available resources combined with external inputs”.

1.0 INTRODUCTION TO CONSERVATION AGRICULTURE

2

3

The key aspects to conservation agriculture include soil restoration and preservation through reduced

soil movement, soil surface cover through mulch and crop interactions and associations to maximize

water infiltration but minimize run off. Mulch may be defined as any plant materials such as crop residues

that may be used to cover the soil surface. Conservation agriculture ensures more efficient utilization of

inputs such as fertilizers and chemicals in order to achieve optimum yields without damaging the

environment.

There is evidence that farmers who use conservation agriculture technologies in their farming tend to

attain higher yields than those who practice conventional farming. Some work carried out in the small

holder sector in Zimbabwe has shown that yields of crops have increased substantially following the

adoption of conservation agriculture methods (Zimbabwe Conservation Agriculture Task Force, 2009).

However, other factors such as early planting and improved management could also have contributed to

these results.

While the practice is applicable to both small scale and large scale farming, it is perhaps in the

smallholder sector that quick positive results can be achieved. This is because many smallholder

farmers have a serious lack of resources such as draft cattle, fertilizers and other necessary inputs which

may cause delays in planting. When farmers adopt conservation agriculture, the labour requirements to

work one hectare of land diminish with time while yields increase.

Traditional farming methods, particularly ploughing each year to prepare the land for planting (and this is

so common in many of Zimbabwe's communal lands), are definitely not achieving the production levels

so much required by the country. Annual ploughing of land often leads to serious loss of soil and the

reduction of that soil's potential to produce in subsequent seasons. These traditional land preparation

methods may, therefore endanger food security.

The frequent occurrence of drought in Zimbabwe emphasizes the need to practice water conservation

approaches in our farming, particularly in comparatively dry areas. Water harvesting techniques may be

an option.

4

These trap water, direct it to the root zone and minimize run off. And where there is little rainfall received,

most of it will be trapped thus benefiting the crop. This can make the difference between a harvest and a

complete crop failure.

The general shortage of inorganic fertilizers in recent years has shown the need to consider utilizing crop

residues and other organic materials as much as possible in an attempt to provide and recycle essential

nutrients and to reduce water loss through evaporation from soils.

In conclusion, conservation agriculture is about sustainable use of natural resources and harnessing of

natural biological processes for better food production. It is an approach in farming that attempts to

minimize waste and use of external inputs but at the same time ensuring food security.

1.4 Conservation Agriculture Principles, Advantages and Challenges:

Conservation agriculture takes advantage of natural ecological processes to conserve moisture,

enhance soil fertility, improve soil structure and reduce soil erosion. These benefits are achieved through

the application of the following three key principles:

?Minimum mechanical soil disturbance

?Maintenance of soil cover using organic material,

?Use of crop rotations, associations and interactions.

The above three principles combined with appropriate agronomic management practices result in

timely and precise farming operations which ensure efficient use of inputs and impact positively on crop

productivity.

Minimum Soil Disturbance

This principle aims at reducing soil disturbance as much as possible. The objective of minimum soil

disturbance is to create only a hole or an opening in the soil where the seed will be placed at planting.

The advantages of such an approach include:

(a) Reduced fuel-energy and labour inputs. Less fuel energy is used as only a small fraction of

the land is worked on. Up to 70% savings in fuel have been reported (FAO, 2008).

5

(b) Reduced exposure of the soil to the elements of weather, particularly run off after a heavy

storm.

(c) Reduced wind erosion of the soil which is commonly observed in conventionally ploughed

fields.

(d) Improved water infiltration through the retention of crop residue or other organic matter as well

as biopores from previous root channels, termites and earthworms. If only planting holes or

basins are made in the ground or where a deep planting channel has been created by a chisel

plough, there will be optimum water penetration into the soil.

(e) With time, less exposure of weed seeds to the soil surface where they would normally

germinate.

(f) Reduced destruction of soil structure.

(g) Reduced evaporative loss of moisture from upper soil layers. The soil moisture within the

upper soil layers is not exposed to the surface from where it can evaporate. This moisture

remains within the soil as it is not brought to the surface.

(h) Slow oxidation of soil organic matter, thereby reducing release of carbon dioxide into the

atmosphere. The soils which are most vulnerable to tillage-related loss of organic matter are

those of coarse texture and where the clay fraction is dominated by low- activity clays. Such

soils ( e.g., ferralsols, cambiosols) are widely distributed in the tropics and subtropics and total

over 750 million ha (FAO, 1978-1981; Higgins and Kassam, 1981).

(i) Minimum disruption of biological activities of organisms below the soil surface. The soil

capacity to favour root growth and water transmission is maintained through the activities of

soil organisms when they are sufficiently provided with organic matter, water and nutrients.

The results of these activities are the creation of channels which will improve water infiltration

and aeration.

6

The sustainability of the soil's productive capacity depends on the influence of soil organisms

on the soil- aggregate re-formation, and hence, unnecessary tillage increases the rate of biotic

activity and the break down of the organic matter on which the organisms depend. If the rate of

soil physical degradation exceeds the rate of its re-formation due to soil organisms, its

penetrability by water, roots and gases diminishes, productivity declines and run-off and

erosion increase.

(j) Reduced soil compaction and surface sealing (crusting) by rain drop impact.

Mulch Cover

This involves the maintenance of year-round organic matter cover over the soil, including specially

introduced cover crops (e.g. cow peas) and has the following beneficial effects:

a) Reduced evaporative loss of moisture from the soil surface.

b) Minimized compaction by intense rainfall, passage of feet and machinery.

c) Minimized temperature fluctuations at soil surface

d) Maximizing rain infiltration and minimizing run-off and soil loss.

e) Reduced weeds

f) Re-building of damaged soil conditions and dynamics through supply of organic

matter/carbon.

g) Providing substrate for soil life.

Crop Rotations and Interactions

Crop rotation is a practice of ensuring that crop families are not repeatedly grown on the same land each

year. The plant groups involved are root/tuber, leaf, legume and grain crops, deep and shallow rooting

plants.

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Intercropping is a farming practice where two or more crops are grown together on the same piece of

land. Intercropping is one of the oldest cultural practices in many parts of Africa and also in other parts of

the world. As a general practice, the crops that are grown in the same field will include a grain crop such

as maize or millet and a legume crop such as cow peas, sugar beans and groundnuts or another ground

covering crop such as pumpkins. It can be any combination depending on the requirements of the

household.

The advantages of intercropping are obvious from the food supply point of view, particularly in the

smallholder situation. Traditionally, farmers did not have mono- cropping but would try to produce the

main food crops on the same piece of land. Diversification of crop rotations, sequences and associations,

adapted to local environmental conditions, and including appropriate nitrogen-fixing legumes have the

following advantages:

a) Maintaining biodiversity above and in the soil.

b) The legumes contribute nitrogen to the soil-plant system.

c) Reduce the build up of pest populations.

d) Inter - crops or cover crops form canopies on the ground that protect the soil from erosion and

weed growth for the benefit of both crops. In this case, the soil conservation aspect comes out

clearly.

e) The cover provided by the legume crop improves water infiltration for the benefit of the two crops.

f) Crops with different rooting characteristics can explore and recycle nutrients from different parts of

the soil.

g) The harvesting of both the grain and the legume offers a balanced diet to the household.

h) The grain crop provides support to the climbing legume crop and thus improves access to sunlight

and gives strength to the plant (legume) leading to higher productivity.

I) Where a household produces excess pulses, these can be sold for cash or some other product

that is needed in the family.

j) The stover from a combined cereal/legume crop has greater nutritive value to livestock than that

from the cereal alone.

8

Climate Change in Conservation Agriculture

With reference to climate change, conservation agriculture can play an important role in ameliorating the

effects of drought and extreme temperatures (high or low). The occurrence of drought in the Southern

African region is increasing, thereby leading to a reduction in both crop and livestock production.

Applied at watershed level, conservation agriculture, through better rainwater infiltration can also reduce

the risks of flashfloods and inundations and sedimentation of mud downstream which result from

excessive surface runoff.

Challenges in Conservation Agriculture

The following are challenges that may be experienced in implementing conservation agriculture:

Weed management may be a problem in the first two years of practice. This problem may be

solved through careful and shallow hand weeding and use of herbicides (which may present an

additional cost) or, alternatively, the use of a cover-crop to suppress excessive weed growth.

Competition with livestock for crop residues which are used as mulch on crops. The provision of

feed from other sources or the careful balancing of the residues used for fodder and for mulch may

assist in overcoming this challenge.

Carryover of diseases and pests through retention of crop residues on the land especially where

mono-cropping is practiced. This challenge may be reduced by practicing crop rotation and

through build up of natural enemies of pests through biological and ecological processes.

Crop residues may encourage the build-up of termites in the fields which may lead to crop lodging

and grain loss.

Accumulation of stover on the land may impede the use of machinery such as planters and rippers

which may not be appropriately designed for the environment. The use of appropriately designed

machinery can overcome this problem.

During the first two years of practicing conservation agriculture, there may be very little economic

benefits. This results often from the high labour cost of establishing conservation agriculture

practices such as digging pits, hand weeding and mulching.

9

However, using adequate technologies and appropriate technical advice, for example shallow

weeding and use of cover crops, the labour requirements can be reduced from the very

beginning.

?Farmer preferences and market demands for crops may present a challenge in implementing the

crop rotation practices. Assistance in marketing can overcome this problem.

1.5 Activities:

i. Demonstrate the effect of mulching on water infiltration and soil erosion using laboratory models.

ii. Visit a farm or centre where conservation agriculture is taking place.

iii. Establish own conservation agriculture plot where the principles mentioned in this chapter can be

put into practice.

iv. The college to establish outreach programs with local farmers where the concepts of CA can be

put into practice. The college to monitor and evaluate the outreach projects.

1.6 References:

Goddard, T., Zoebisch, M.A., Gan, Y.T., Ellis, W., Watson, A. and Sombatpanit, S.(eds) 2008. No-Till

Farming Systems. Special Publication No. 3, World Association of Soil and Water Conservation,

Bangkok,

Nyagumbo I.and Mugabe, F.T., 1999: Self Study Material for drought mitigation in rural Zimbabwe,

Water and Soil Conservation with drought in mind; Swedish Cooperative Centre, Harare

Vowles, M., 1989: Conservation Tillage, A Handbook for Commercial Farmers in Zimbabwe; Laser Print

and Cannon Press, Harare

Zimbabwe Conservation Agriculture Task Force, 2009, Farming for the Future, A Guide to

Conservation Agriculture in Zimbabwe

10

2.0CONSERVATION AGRICULTURE OPTIONS AND APPROPRIATE TECHNOLOGY

(4hrs theory & 8hrs practical)

2.0 Aim : To acquaint students with the various options of conservation agriculture that can be used by

farmers

2.1 Objectives:

At the end of the topic, students will be:

i. able to describe the application of different technologies of conservation agriculture such as

planting basins, shallow basins and direct seeding,

ii. aware of the advantages and disadvantages of the various technological options for

conservation agriculture,

iii. able to make recommendations of appropriate technologies for conservation agriculture in

various farming situations.

2.3 Manual Conservation Agriculture Tillage Systems:

Planting basins

Planting basins are a key component of conservation agriculture in Zimbabwe, particularly in the

smallholder sector. The basins are dug in straight lines, spaced at the desired row spacing, which may be

75cm in Natural Regions II and III or 90cm apart for drier environments (Figure 1).

Each basin should be 15cm wide, 15cm deep and 15cm long. Within a row, the basins should be spaced

60cm apart. At planting, the number of seeds placed per basin should match the final plant population

desired. For maize, three seeds are planted to give the target population of 40 000 to 60 000 plants per

hectare after thinning.

Figure1. Planting basins dug out in a field ready for planting. (Adopted from FAO publication)

11

The following are the key advantages of using the planting basin:

?The farmer prepares the land long before the rainy season begins.

?Only a relatively small percentage of the field surface area (4-17%) has to be prepared (compared

to hoeing the entire field).

?Manure and planting fertilizers (compound D or equivalent) can be placed in the basin with greater

precision compared to conventional methods.

?Rain will collect in the basin, thus increasing the effectiveness of each fall, particularly where low

rainfall is experienced. The effect of drought is, therefore, minimized.

?Planting of the seed can commence immediately after the first rains have fallen or even before.

?The same basins can be used each year thereby saving labour and making use of established root

channels in the planting stations.

Farmers using planting basins in Zimbabwe have generally achieved higher yields than other farmers

still using the conventional methods. The main reasons for this relative success lie in the fact that:

(i) Farmers using planting basins plant their crops early. The season's rainfall is, therefore,

utilized to optimum capacity. Under conventional systems, farmers use the first rains to plough

their lands, sometimes delaying actual planting by as much as two to three weeks. This

compromises yields.

(ii) There is efficient utilization of the season's rainfall for the growth of the crop. Water is trapped

in the basins and this is very critical in a drought year, where every drop of rain that can be

saved for the crop counts.

(iii) Weed removal can start soon after planting, targeting the areas around the basins, leading to

an efficient control of the weeds.

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(iv) Organic manures are placed in the basin where they will decompose and with time benefit the

crop. A relatively lower quantity of inorganic fertilizers will therefore be used.

Planting basins are an appropriate method of farming, particularly for smallholder farmers who lack

resources such as draft animals and related implements generally used in that sector. The key aspects

are that farmers can plant their crops earlier using basins and achieve a harvest that may well exceed

that of other farmers using conventional methods.

The following are disadvantages of planting basins:

i). The labour requirements to dig the initial planting holes may be prohibitive to the adoption of the

method, particularly where there are elderly household members or chronically ill members

ii). In seasons where excessive rain falls, there may be a challenge of water logging and leaching of

nutrients down below the rooting zone.

Shallow planting holes

These are similar to planting basins but are shallow and designed for the planting of small grains such as

sorghum and millets, which require shallow planting depths. The shallow holes measure approximately

5 to 10 cm in length and are 2 to 5 cm in depth. The establishment of these holes is carried out during the

dry season before the arrival of rains. As soon as enough rains have fallen, the farmer can plant the

required amount of seed in the basins.

The advantages are similar to those of the planting basins for the larger seed crops discussed above,

i.e., early planting, maximum utilization of the season's rainfall, reduced erosion, improved infiltration of

rain water and an increased yield.

The challenges are similar to the ones mentioned in the preceding section on planting basins.

Jab Planters

These are hand-held direct seeding implements that usually have both fertilizer and seed hoppers and

can therefore place both seed and fertilizer at the same time.

13

The use of jab planters is not widespread in Zimbabwe because of the unavailability of good quality jab

planters and the skilled operators. While the future use of jab planters appears hopeful, there is still a lot

of work to be done to make them more user friendly.

2.4 Ox –drawn CA Tillage Systems

Ripper Tines

Farmers who have draft cattle and the traditional plough can fit a ripper tine to the frame of the mould

board plough and open lines or channels in the ground into which planting of seed can be carried out. It is

not difficult to fit these tine rippers on the plough frame.

Ripping reduces soil exposure and also facilitates water penetration in the ripped line. Fertilizers and

seed are placed in the ripped line according to the desired rates. Ripping in a field with a good cover of

mulch or stover from the previous crop is most rewarding.

The advantages of the tine ripper method as a form of tillage are as follows:

The ripper is drawn by draft animals such as cattle, donkeys or mules and is a faster

method of land preparation compared with conventional mould board ploughing.

It is a method that uses less fuel or energy per hectare and is therefore desirable.

The ripped lines are spaced according to desired row spacing at planting and there is

therefore no need to mark planting rows. In conventional tillage, ploughing is first done

followed by marking lines for planting and this wastes time and energy.

The method reduces water run off, thus minimizing erosion.

By ripping, the efficiency of trapping water in the field is improved and this is important in a

drought year or in the drier areas of the country.

Using the ripper tine is therefore another suitable conservation farming method for farmers who have

draft animals and can afford a mould board plough. It is an energy saving method and also a water

conservation method.

14

Ox- drawn direct seeder

Figure 2 below shows an ox-drawn direct seeder. This implement has a ripper tine fitted in front of the

seeder unit. Under suitable soil conditions, the farmer will be able to open a channel in the soil and plant

with the same implement thus saving labour costs substantially. Direct seeders place seed and fertilizer

in one operation thereby saving time and labour.

Figure 2. Direct ox-drawn seed drill

2.5. Tractor drawn conservation agriculture tillage systems

The principles of conservation agriculture that apply to small holder farming also apply in the large scale

farming sector where various machinery exists and can be adapted for conservation agriculture work. A

tractor can be used conventionally where the whole field is ploughed or ploughed and disked, thus

exposing the soil to erosion and other problems such as compaction and capping. In order to minimize

these problems, farmers can use a number of reduced or zero tillage techniques and these include

rippers or sub-soilers with narrow chisels and direct seeders.

Tractor drawn ripping equipment

Figure 3 shows a ripper which rips a deep furrow in the ground where seed can later be placed. The

ripping and planting can be done at the same time provided a seed drill or planter is drawn in tandem with

the ripper. The control of weeds can be carried out by spraying the appropriate herbicide thus reducing

hand labour.

This tillage method has the following advantages:

?There is minimum soil disturbance, particularly the surface structure

?Less energy is used per hectare for land preparation.

15

?The ripping shatters compacted soil horizons, where they exist and creates a suitable

environment for root development.

?Water penetration into the soil is greatly improved through the ripped lines, thus increasing

survival of the crop during dry spells.

?Run off is markedly reduced in the event of a storm occurring.

?With time, it is known that the soil structure is improved than if conventional methods were used.

Figure 3. Chisel ripper

Direct Planting

In these methods, there is minimum soil disturbance as the aim is to plant directly into the untilled land or

into the previous crop residue or stubble. There is, therefore, very minimal soil distance, the only

alterations to the soil surface being the creation of the planting holes or lines (Figure.4).

Advantages of direct seeding include the following:

?The method provides the least disturbance of the soil.

?The previous crop residue or stubble protects the soil from wind and water erosion.

?The stubble enhances water conservation and this is important in a drought year or when a dry

spell is being experienced.

16

?The stubble or crop residue contributes to improvement of soil texture and fertility.

?The stubble offers protection from direct sun heat and from physical damage to the germinating

seedlings. This protection is not available in conventionally prepared crop fields.

?The minimum disturbance of the soil reduces the weed pressure and soil moisture losses.

Figure 4. Jab Planter

2.6 Activities:

i. The college to visit a farm that is practicing conservation agriculture.

ii. Students must be exposed to the operations of various implements used in CA.

iii. Students to learn CA methods using the machinery for conservation agriculture at the College's

demonstration plot.

17

iV. The college to establish outreach programs with local farmers where the concepts of CA can be

put into practice. The college to monitor and evaluate the outreach projects.

2.7 References:

Baker, CJ, Saxton, KE, Ritchie, WR, Chamen, WCT, Reicosky, DC, Ribeiro, MFS, Justice, SE, Hobbs,

PR 2007. No-tillage seeding in conservation agriculture; Baker, CJ and Saxton KE (eds.), 2nd rev. edition

of No-tillage seeding, 1996; CABI/FAO, 326p.

Goddard, T., Zoebisch, M.A., Gan, Y.T., Ellis, W., Watson, A. and Sombatpanit, S.(eds) 2008. No-Till

Farming Systems. Special Publication No. 3, World Association of Soil and Water Conservation,

Bangkok,

Li Rui, 2008. An Overview of Soil and Water Conservation and Dryland Farming.Paper presented at an

International Seminar on Soil and Water Conservation and Dryland Farming, June 2008. Yangling

International Exchange Center, China

Nyagumbo, I. and Mugabe, F.T., 1999. Self Study Material for drought mitigation in rural Zimbabwe:

Water and Soil Conservation with drought in mind; Swedish Cooperative Centre, Harare

Vowles, M., 1989. Conservation Tillage, A Handbook for Commercial Farmers in Zimbabwe; Laser Print

and Cannon Press, Harare

Zimbabwe Conservation Agriculture Task Force, 2009. Farming for the Future, A Guide to

Conservation Agriculture in Zimbabwe

18

3.0 CROP AND LIVESTOCK INTERACTIONS IN CONSERVATION AGRICULTURE

(4hrs theory & 8hrs practical)

3.1 Aim: The topic is to make agricultural college students appreciate interactions of crops and

livestock in Conservation Agriculture (CA).

3.2 Objectives: At the end of the topic, students will be able to:

i. situate crop and livestock production in Conservation Agriculture systems,

ii. describe crop and livestock interactions that exist in Conservation Agriculture systems,

iii. manipulate crop and livestock interactions in order to improve and sustain agricultural

production in Conservation Agriculture systems.

3.3 Agricultural Ecosystem

Conservation Agriculture (CA) is ecological. It involves the judicious and methodical

manipulation and management of components of the agricultural ecosystem such that the soil-

plant-animal complex is protected and enhanced. The ultimate objective is to attain sustainable

food security, bearing in mind that the ultimate source of all food is solar energy which is stored by

photosynthetic (green) plants (Figure 5).

Figure 5. Agricultural ecosystem (Adapted from Stoddart, Smith and Box, 1975)

30 Consumers

20 Consumers

10 Consumers (herbivores)

1. Herbage2. Grains3. Animal products

10 Producers (green plants)

Erosion products

(soil and nutrients)

………………………………………

Biotic factors (players) Abiotic factors (controllers)

1. Microbial activity (decomposers) 1. Soil (fertility, structure, moisture)2. Plants (competition) 2. Topography/exposure3. Animals (grazing) 3. Climate (rainfall, temperature,4. Humans/management factors light, humidity, gases, wind)

4. Fire (controlled, uncontrolled )5. Organic matter/litter

Death and decomposition

Harvest

FOOD SECURITY

LAND

The basic principle of farming is to change the natural ecological system into one which produces

more of the goods desired by man. The major problem of farming in the tropics and subtropics is

maintenance of soil fertility. Conservation Agriculture aims to solve the problem by mimicking the

natural forest environment and applying the principles of soil cover, minimal soil disturbance and

diversity of crops.

19

20

Although CA is essentially crop-based, livestock are an integral part of most CA systems. While the

livestock contribute to human well-being by providing meat, tallow, milk, hides (leather), wool (fibre),

horns, draught power and manure for fuel and fertilizer, the crops provide feed for the livestock. Cereal

and legume grains underpin monogastric (pig and poultry) and intensive ruminant (sheep, goat, dairy

and beef) livestock production. Forages or roughages, which include natural pastures (veld), permanent

and temporary improved pastures, browse, fodder, green chop, hay, silage and crop residues, provide

the major source of feed for ruminant livestock. In the following paragraphs, the interactions of crops and

livestock in CA systems are elaborated.

3.4 Competition for crop residues

Crop residues (stover) are those plant parts that remain following harvest of the main economic product

such as food grains. Plant residues are a major source of soil cover in crop fields, which is a key principle

of CA. However, the residues are also an important feed for ruminant livestock which form an important

and integral part of most CA systems in Zimbabwe. The dry season, is a critical period of competition for

crop residues. Strategies that help in alleviating the competition for crop residues are given in the

following paragraphs.

Cattle may be allowed limited gleaning of the more nutritious portions of crop residues, leaving the bulk of

the less nutritious material as mulch.

Natural pastures (veld) can provide the bulk of forage for ruminant livestock if well managed, hence

reduce the competition for crop residues. Production of forage from veld can be improved through proper

stocking rates, controlled grazing, bush control and legume reinforcement.

Additional forage can be provided by growing fodder crops such as nappier fodder, bana grass and

leucaena in alleys, contour bunds or other arrangements. Cover or forage crops that are grown in

association with main crops can also be used either directly as fodder or by providing soil cover thereby

allowing removal of some of the crop residues. Pasture legumes and grasses can also be incorporated in

crop rotations to provide forage while improving soil fertility.

Surplus forage may be conserved in the form of stored hay and silage which can be used during periods

of fodder shortage. If of poor quality, the hay can be improved by treating with urea.

21

Transfer of plant nutrients

The concept of conservation agriculture discourages livestock from uncontrolled grazing on arable

lands. However, there are certain benefits obtained in allowing animals to graze on the arable lands such

as deposition of dung and urine. These two products add nutrients to the soil though not evenly

distributed.

3.6 Draught power provision

Draught animal power speeds up field operations and is cheaper than tractor power. The demand for

draught animal power is much less with conservation agriculture relative to systems based on

conventional tillage.

3.7 Competition for land

Conservation agriculture may improve crop yields thereby freeing up more land for livestock grazing and

forage production.

3.8 Livestock Manure and Compost as Alternative Fertilizer In Conservation Agriculture

Livestock manure is a mixture of the dung and urine of animals. The common sources of farmyard

manure are cattle, goats, sheep, poultry, pigs and rabbits. Maintaining soil fertility is the major problem of

farming in the tropics because OM decomposes rapidly, making it difficult to maintain and increase soil

OM. Manure has a long-lasting (residual) effect on crop production though its concentration of nutrients

is low. Application of manure will increase OM, increase soil nutrients, increase cation exchange

capacity, increase biological activities, ameliorate soil acidity (increase soil pH), moderate soil

temperature and improve physical properties of the soil such as soil structure, bulk density, water

infiltration and water-holding capacity. Thus, manure improves the physical, chemical and biological

properties of the soil and reduces the risk of crop failure. Both dung and urine contain nitrogen (N),

potassium (K) and phosphorus (P) but those in urine are more readily available (soluble) than those in

dung. The value of animal manure varies with the type of animal and the nature of the feed eaten by the

animal. Feeds that are richer in elements essential for plant growth produce more valuable manure.

Manure of mature animals is richer than that of young animals which are still forming bones and muscles.

The value of the manure also varies according to the product the animal produces, for example milk

contains considerable N, P and K while wool contains considerable N.

Losses of N from manure through volatilization as ammonia and leaching as nitrates can be as high as 40

to 99%. The losses from volatilization can be reduced by reducing the pH of the manure and by adsorbing

ammonium-N on organic materials.

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Thus mixing N-deficient organic materials with manure, e.g. 3 parts straw: 25 parts manure, can reduce

N losses by as much as 85%. Manure output can be increased by supplying the animals with more feed

while better use of N in urine can be obtained by bedding animals on straw which absorbs the urine.

The value of manure can be enhanced by composting. Compost is a mixture of decomposing (decaying

or rotting) vegetation, manure and other OM that is used to fertilize the soil. There are various methods

and techniques of composting. Good compost can be made from plant residues when at least 20 to 25%

of the heap is manure. Composting involves the biological reduction of organic wastes to humus. Humus

is the relatively stable end-product of composting which builds the soil and is rich in nutrients and OM.

Direct addition of manure to the soil usually has an adverse effect on crops due to the instability of its

carbon (C) to N ratio. For example, there may be too much urine and too little cellulose or vice versa. The

imbalances can be rectified by composting. Rotted manure is richer in plant nutrients mainly due to loss

of about one half of its weight during rotting. The N in rotted manure has been fixed by microorganisms

while that in fresh manure is mostly soluble. The solubility of P and K is greater in rotted manure. Thus,

composting produces an ideal medium for plant growth, conserves nutrients and also kills weed seeds

and disease organisms.

The benefits of compost and composting are numerous. Compost builds good soil structure (crumbs or

aggregates) for aeration, water drainage, water-holding capacity (water absorption and retention).

Compost protects crops against drought. Water is soaked up like a sponge and stored on the soil

crumbs: 100 kg of humus holds 195 kg of water. Compost controls erosion because soil that lacks crumb

structure is susceptible to erosion. Compost improves soil aeration. Compost is a source and storage of

nutrients: the nutrients are released over long periods of time and the rate of release is depends on

temperature. Slow release leads to build up of soil fertility. Compost neutralizes toxins because OM has

a high capacity to fix heavy metals such as aluminium which may interfere with uptake of P. Compost

controls pH: earthworms feed on compost and moderate the pH of soil and OM that pass through them.

Compost stretches the growing season by making soil darker, thereby absorbing more heat from the sun

and extending the growing season into the cooler months.

During the process of composting, temperature rapidly rises at first and then cools down when the

readily decomposed substrate is finished. The finished compost, therefore, is cool and contains simple

sugars, organic acids, ammonium compounds, nitrites and nitrates.

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Environmental factors affect composting. Decomposition can be aerobic or unaerobic. The minimum

moisture for bacterial activity is 12 to 15%, but generally, moisture content becomes limiting below 45 to

50%. Most compost start off at mesophilic temperatures (10 to 45 degree C) and rise to the thermophilic

range (45 to 70 degrees C). The high temperatures kill weed seeds and diseases of plants. A pH range of

6.0 to 7.5 is preferred by bacterial decomposers, 5.5 to 8.0 by fungal decomposers and 7.0 in finished

compost.

Large fauna such as mites, millipedes, centipedes, snails, slugs, spiders, beetles, ants, flies, nematodes,

flatworms and earthworms physically decompose organic materials by biting, chewing, grinding, sucking

and tearing the materials into smaller pieces for microscopic decomposers. The microscopic organisms

(actinomycetes, fungi, protozoa and bacteria) chemically break down the materials further.

Actinomycetes are a higher form of bacteria similar to fungi and molds. They produce antibiotics, are

important in humus formation and give the earthly smell of newly ploughed soil. However, the most

important compost decomposing organisms are bacteria and earthworms.

The earthworms enhance the quality of compost. They are capable of consuming their own weight of soil

and OM per day. The earthworms ingest, decompose and excrete rich compost (casts). The castings of

the worms contain 5 to 11 times the amount of available N, P and K as the soil the worms ate to produce

the castings. The humus is of a very rich quality. The earthworms also mix, aerate and hasten decay of

OM.

3.9 Activities

i. Students should conduct research on and establish compost heaps using various methods and

techniques. Apply the manure onto CA plots.

ii. Establish at the College a conservation agriculture set-up that demonstrates crop and livestock

interactions. Critically investigate and analyze the productivity of the set-up and draw up

conclusions and recommendations, especially on soil properties.

iii. Students to grow fodder crops

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3.10 References:

Dzowela, B.H. and Shumba, E.M. (eds) 1993. Agroforestry Research and Development in Zimbabwe:

Proceedings held at the University of Zimbabwe, 3 – 5 March 1992. National Agroforestry

Steering Committee, Harare.

Kassam, A., Kueneman, E., Kebe, B., Ouedraogo, S., Youdeowei, A. 2009. Enhancing Crop-Livestock

Systems in Conservation Agriculture for Sustainable Production Intensification, Integrated Crop

Management Vol. 7-2009, FAO/Rome

Landers, J.N., 2007. Tropical crop-livestock systems in conservation agriculture, The Brazilian

experience, Integrated Crop Management Vol. 5-2007, FAO, Rome

Ndlovu, L.R. and Francis, J. 1997. Performance and Nutritional Management of Draught Cattle in

Smallholder Farming in Zimbabwe. University if Zimbabwe Publications, Harare.

Matizha, W. 2002. A Comparative Nutritive Evaluation of Three Tropical Forage Legumes Grown

Successfully by Farmers in Zimbabwe. D. Phil. Thesis, Faculty of Agriculture, University of

Zimbabwe, Harare.

Matizha, W., Clatworthy, J.N. and Kangai J.R. 1995. Effect of stocking rate on

beef cattle performance and vegetation changes on Hyparrhenia veld reinforced with fine-stem

stylo. Zimbabwe Journal of Agriculture Research 33 (1): 23 – 38.

Matizha, W., Clatworthy, J.N. and Maclaurin, A.R. 1993. The use of Leucaena

leucocephala pasture as a supplement for growing cattle grazing a basal pasture of Panieum

maximum and herbaceous legumes in Zimbabwe. Zimbabwe Agricultural Journal.

Starkey, P., Mwenya, E. and Stares, J. 1994. Improving Animal Traction Technology. Proc. Animal

Traction Network for Eastern and Southern Africa, 18-23 January, 1992, Lusaka, Zambia. CTA,

Wageningen, The Netherlands.

Stoddart L.A., Smith, A.D. and Box T.W. 1975. Range Management. McGraw-Hill,Inc., New York.ndValentine J.F. 1980. Range Development and Improvements (2 ed). Brigham Young University Press.

Provo, Utah.

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